1. Field of the Invention
This invention relates to a device for orienting a disc having a flat portion on the outer periphery thereof.
2. Description of the Prior Art
Various devices for orienting a disc having a flat portion formed on the outer periphery thereof, for example, a wafer for the manufacture of a semiconductor circuit element, have heretofore been proposed.
For example, U.S. Pat. No. 3,297,134 discloses a device for orienting a disc by urging the flat portion of the disc against a flat surface. U.S. Pat. No. 3,865,254 discloses a device for orienting a disc having a flat protion by rotating the disc. U.S. Application Ser. No. 970,146, abandoned in favor of Application Ser. No. 256,173, covers a device in which said two devices are combined so that rough position adjustment and fine position adjustment of a disc are effected in two stages. However, the device of this copending application effects the rough position adjustment and the fine position adjustment in different stages.
The present invention relates to a device for effecting the rough position adjustment and the fine position adjustment in one and the same stage.
However, the device for effecting the rough position adjustment and the fine position adjustment in one and the same stage is known per se. Since such device has a deep relation with the device of the present invention and applicant does not have the publication which describes such device, it will be described by reference to FIGS. 1 and 2 of the accompanying drawings. In these Figures, reference numeral 1 designates a wafer. This wafer is carried onto an orienting base plate 2 by wafer conveying means, not shown. The wafer thus conveyed faces in any direction as indicated by 1'. Air supplied from an air supply port 7 is blown off toward the surface of the base plate 2 through a plurality of inclined holes 8 to float up the wafer 1' and urge the wafer 1' in the direction of arrow. Accordingly, the wafer 1' has a portion of its periphery brought into contact with a driven roller 4 and a drive roller 3 and starts to rotate with the rotation of the drive roller 3.
Finally, the wafer 1' completes its orientation by a point on the circular circumferential portion thereof contacting the driven roller 4, a point on the straight portion thereof contacting the drive roller 3 and the intersection between the circular circumferential portion and the straight portion contacting a fixed block 5. That is, when the wafer has been rotated to this position, the drive of the drive roller 3 is stopped by a photoelectric switch 9 to stop the rotation of the wafer. By this stoppage, the rough position adjustment of the wafer is accomplished. At the same time, the fine position adjustment of the water 1 is effected since the wafer is urged against the driven (rotating) roller 4 and the drive roller 3 by the air from the air supply port 7. However, where the wafer is in the state as indicated by 10 at the point of time whereat the drive roller 3 has been stopped, a reaction force for the water urging force by the air is produced at the points of contact between the driven roller 4 and the drive roller 3 and the wafer and when an attempt is made to rotate the wafer to its final position, a torque is produced. On the other hand, a friction force resulting from such reaction force acts in a direction to block the rotation of the wafer. The drive roller 3 is directly connected to a drive source (a motor or the like) and therefore, its rotational torque is great and thus, sliding friction acts at the point of contact between the drive roller 3 and the wafer and the rotation blocking torque often becomes greater than the rotational torque and thus, the wafer completes its orientation in the state as indicated by 10, which has been a factor for aggravating the accuracy of orientation.
The same thing may also occur when the drive roller 3 is stopped with the wafer being in the state as indicated by 10'.